No. The switch over was above 4.10. 4.10 still used standard carrier. 4.56 needed the spacer or different carrier.
Could be true, but for all we know the 4.10 gears that are in it NOW were not the driving factor for the lack of BOM numbers on the axle from 50 years ago. The statement from the service manual is still a possible explanation for the lack of BOM numbers on this axle.
Is true, not could be. Look at the options available from purchase books. Look at the Parts manual. You could get a 3.54 or a 4.10 gear. The Dana differential case supported both. The Race literature and the Dana documents support, along with anyone who has raced one or rebuilt them, that the switch over to a different case is 4.56. This gear has a much smaller pinion and the ring gear is required to move over about 1/4". They had a case with a thicker mounting flange, or racers would weld on a spacer plate to shift the ring gear over. The higher ratio was a a dealer available option, but only the carrier was changed with the gear, not the axle housing.
I know you want this to be a factory line part, but I think the wisdom is that production cars had Dana's with the known BOM numbers. Either 3.54, or 4.10. Getting a 4.10 did not require the axle housing to be changed or the differential carrier.
You have a Dana. Maybe some one knows what the BOM was if you bought a housing from a dealer. You number is more like a Dana part number then an assembly BOM.
Go to the spicer website and you can access the parts catalogs for the 68-78 Dana rears for Dodge/Plymouth, and the other manufactures that used it.
